Ultrastructure of Bruch's membrane after krypton laser photocoagulation. I. Breakdown of Bruch's membrane.

Previous observations on rats suggested that subretinal neovascularization does not require a prior break in Bruch's membrane (BM). We verified this observation by using scanning electron microscopy to examine large expanses of BM that became exposed following ophthalmoscopically white krypton laser burns. Bruch's membrane appeared intact in the acute phase after injury. Subsequently, slitlike defects in BM were associated with penetrating choroidal capillaries. These observations were consistent with transmission electron microscopic findings of cellular protrusions arising from the choriocapillary endothelial cells and from regenerating retinal pigment epithelial (RPE) cells invading BM. These cell-formed defects in BM differed from thermal defects in appearance, size, and onset of occurrence. Endothelial cells penetrated all layers of BM, including the RPE basement membrane. We conclude that endothelial cells can erode their own basement membrane and the RPE basement membrane, and krypton laser burns with or without immediate rupture of BM induce cellular activity that may result in defects in BM.